Alternative voltammetry on self-assembled monolayers: An original approach to estimate the electrochemical electron-transfer rate constants when electroactive adsorbed species interact

Abstract

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Cover Feature: Electron Transfer Inside a Decaferrocenylated Rotaxane Analyzed by Fast Scan Cyclic Voltammetry and Impedance Spectroscopy (ChemElectroChem 18/2021)

“…Considering that the density of redox centers is low and that a large supporting electrolyte concentration is used, we will below neglect their interactions even if we are aware that this may be an oversimplification. [14] In the following, in order to examine more deeply the origin of this slight discrepancy, we complement the CV results with impedance ones performed onto exactly the same modified electrode and under the same conditions. Indeed, impedance provides the possibility to examine the behavior of a system at a given potential and is thus complementary to cyclic voltammetry.…”

“…[41,42] For selfassembled monolayers, Creager et al proposed in 1998 impedance as an alternative method to assess electron transfer rates within self-assembled monolayers. [14,[43][44][45] Here, the electrode is polarized at a potential E m , onto which is added a small sinusoidal perturbation of amplitude E, so that:…”

“…[10] More recently, Levillain et al proposed a generalized interaction model that can take into account random or non-random distribution of electroactive centers. [11][12][13][14][15] In all cases, the response tends towards ideality when the surfacic concentration decreases. Nevertheless, despite the care in electrode preparation, monolayers are sometimes not uniform, and present defects such as pinholes [16] or distribution of different environments or distances from the electrode for the redox centers.…”

Analysis of the Electrochemical Response of Surface‐confined Bidirectional Molecular Electrocatalysts in the Presence of Intermolecular Interactions

“…a ¼ Fv RT (37) with v being the voltammetric scan rate. For the case corresponding to absence of interactions, Eqn.…”

“…For these molecules, the presence of intermolecular interactions between the surface confined species is a more logical assumption. [34][35][36][37] These interactions are related to nonhomogeneous solvation of the redox centre, to the appearance of non-effective screening of the coulombic repulsions or to the presence of interactions type p À p, among other situations, [38] and they would affect to the Gibbs energy of the charge transfer process diminishing or increasing the energetic barrier of the transition state. These interactions can be considered from stochastic or phenomenological approaches, with the later being based on thermodynamic isotherms as Frumkin's one.…”